mTOR controls growth and internal architecture of human breast cancer spheroids

mTOR is a serine/threonine kinase participating in two distinct functional complexes: mTORC1 and mTORC2. mTORC1 regulates protein translation, cell cycle progression and autophagy. mTORC2 controls cell survival, proliferation and actin cytoskeleton reorganization. mTOR signaling is often deregulated during breast cancer. We investigated how mTOR and its downstream process autophagy determine the inner architecture of solid tumor aggregates at multiple levels. We focused on structures, which are morphologically altered during progression of cancer, including: nuclei number and volume, cell density, number, shape and volume of polarized structures. We developed a breast cancer spheroid model, in which the effects of mTOR and autophagy modulation were investigated by pharmacological inhibition mTOR signaling and induction autophagy, as well as using ATG7 KO spheroids. Spheroids were imaged with light sheet-based fluorescence microscopy and data were quantitatively analyzed. Our data suggest that mTORC1 regulates the spheroid volume, cell number and size. mTORC2 controls nuclei volume and determines growth and elongation of polarized acini inside a spheroid.